Automatic clutches and automatic transmissions have become more and more widespread. They are activated by means of an actuator system.
The absolute position of such systems is frequently determined here by incremental capturing of the positions of an actuator system by means of an incremental position sensor system.
In patent application DE 10 2005 017 024 A1, which originates from the applicant, a method for performing open-control and/or closed-control of a clutch of an automatic transmission in the drive train of a vehicle is proposed. According to this method, an evaluation criterion is used to qualify a clutch characteristic curve which is used at a particular time, in order to select an adaptation strategy or control strategy as a function of this evaluation criterion. This evaluation criterion constitutes a measure of trust—a trust measure—for the adapted clutch characteristic curve. For example, the trust measure is decreased as a function of the time which has passed since the last adaptation step. It is also proposed that the trust measure he reduced as the adaptation error increases.
DE 10 2006 043 075 A1 discloses a method which provides that a signal is made available which is a measure of the confidence in the absolute position signal or of the reliability of the absolute position signal, and that this signal is set, during or after the detection of a false state, to a value to which a relatively low reliability or a relatively low value for confidence is assigned.
Changes, in particular changes in length in the clutch system, cannot be detected or can be detected only with very great difficulty. This can lead to a situation in which incorrect positions can be unintentionally traveled to by the actuator system, said positions not corresponding to the actual target positions.
This can lead to situations which are critical for safety or which damage the system. The situation which is critical for safety can occur, for example, if a clutch actuator system unintentionally travels to an excessively high position and therefore more clutch torque is transmitted than desired. Within the scope of this document, high positions are to be understood as meaning positions in the region of the closed clutch and low positions are to be understood as meaning positions in the region of the opened clutch.
According to the prior art, when the clutch system is activated or powered up and when it is switched off, referencing is usually carried out, and the absolute position is therefore reconciled with the capturing of the incremental travel. During operation such reconciliation is carried out according to the prior art only if something conspicuous is discovered in the system, such as for example blocking of the actuator or a fault in the capturing of the incremental travel.
The object of the present invention is therefore to ensure that shifts in the actuator system do not lead to incorrect results of the capturing of the absolute travel.
In clutch systems with capturing of incremental travel, the absolute position of the actuator system must take place by summing the increments with the correct sign when changes in position occur.
At a predefined time, a reference position must be traveled to in order to reconcile the incremental capturing of the position with an absolute position which is calculated therefrom.
If shifts occur in the hardware during operation of the actuator system, caused by changes in the hardware or by electrical problems relating, for example, to electromagnetic compatibility (EMC) or reset, this must be detected and a reaction must occur in the form of a renewed reconciliation between the capturing of the absolute travel and the capturing of the incremental travel.
The reconciliation is carried out by what is referred to as referencing. In this context, the mechanical stop of the system is traveled to at a minimum position and the absolute position is set to the defined position value of this stop.
The sequences are controlled by an internal variable, the confidence in the position. If deviations are detected, the method is reduced, and when reconciliation has taken place the confidence is increased again.
The system is fully operationally ready only with a high confidence level. The functionality is restricted when the confidence level is reduced.